On July 10, Vancouver Aquarium fish research scientist Jeff Marliave had the fortunate opportunity to take part in a midwater trawling cruise in Howe Sound with Fisheries and Oceans Canada, aboard the WE Ricker. This was a great opportunity for our research team to continue its surveying efforts in support of the Howe Sound Research Program, one of the Aquarium’s dedicated research initiatives.
On this trip, Jeff’s interest focused on whether adult herring that had spawned in Howe Sound continued to reside there throughout the summer – and therefore, throughout their adulthood. What he found was an interesting development that may resolve some of the mystery around why white-sided dolphins have recently taken up residence in the Sound.
There is a large population of herring from the east coast of Vancouver Island that typically migrates back to the open sea after spawning in the Strait of Georgia. This has led to the conclusion that herring that spawn in abundance in Howe Sound should also be migrating out to open sea at the end of their first year of life. However, on this trip, the Ricker’s net yielded older herring opposite Bowen Island, as well as a high density of two-year old herring in surface waters up by Squamish. One-year old herring were abundant in Ramilles Channel, North of Anvil Island, and underyearling (young-of-the-year) herring were caught everywhere at shallow depths.
In addition to herring, juvenile hake were spotted in abundance at greater depths of the Squamish Reach, north of Porteau – a real surprise. The juvenile hake and the adult herring are all the perfect size for white-sided dolphins to feed on. This may explain why the dolphins have taken up residence in Howe Sound. Other fish species, such as deepsea smelt and northern lanternfish, were caught at greater depths as well. The final surprise of the cruise was the relatively low abundance of young salmon taken in these tows, especially since the target of the cruise was young salmon.
This type of cruise has not been conducted regularly in Howe Sound. Prior to this year, deepwater tows in Howe Sound had not been conducted, so it is not known whether juvenile hake have regularly taken up residence in Howe Sound. It will be interesting to follow the residency of the more easily observed dolphins, especially if this type of worthwhile sampling can be conducted in Howe Sound in future years.
The Vancouver Aquarium’s Howe Sound Research Program is one of five dedicated Aquarium research programs committed to advancing scientific knowledge and conservation planning. Incepted in 1981, the Howe Sound Research Program has conducted both targeted field research and long-term monitoring of habitats and animals in Howe Sound, a roughly 30 by 20 km body of water spanning from Vancouver to Squamish. Exploration of this “living laboratory” has led to research breakthroughs, the identification of conservation issues, and new discoveries of marine life. Program researchers will be sending updates from the field – via AquaBlog – as new discoveries are made.